Production of hydroxyl ions in situ by an electric current in a diffusion transfer process



Jan. 9, 1968 H LAND 7 3,362,

E. PRODUCTION OF HYDROXYL IONS IN SITU BY AN ELECTRIC CURRENT IN A DIFFUSION TRANSFER PROCESS Filed Jan. 11, 1966 EXPOSURE IMPREGNATION ELECTROLYSIS FIG.|

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ATTORNEYS United States Patent 3,362,823 PRODUCTION OF HYDROXYL IONS IN SITU BY AN ELECTRIC CURRENT IN A DIFFUSION TRANSFER PROCES Edwin H. Land, (Iambridge, Mass, assignor to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware Filed Jan. 11, 1965, Ser. No. 519,885 11 Claims. (Cl. 96-29) This invention relates to photography and, more particularly, to a novel procedure for preparing images by diffusion transfer.

A primary object of this invention therefore is to provide a novel system for obtaining transfer images.

Another object is to provide a novel system for obtaining transfer images wherein a photographic assemblage including an exposed photosensitive element is impregnated with a non-alkaline electrolytic processing composition and thereafter a direct electric current is passed between a cathode and an anode that are in contact with the impregnated assemblage to form a transfer image.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and in relation and order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein:

FIGURE 1 is a diagrammatic representation or flow sheet illustrating the novel process of this invention; and

FIG. 2 is a partially schematic perspective view of one electrolytic system useful in the practice of this invention.

Diffusion transfer processes generally involve the steps of developing an exposed photosensitive emulsion with an aqueous alkaline processing composition and forming an imagewise distribution of image-forming constitutents which are transferred, by imbibition, to a superposed image-receiving stratum to form a visible image thereon.

Positive transfer images in silver, for example, may be formed by contacting an exposed silver halide emulsion with an aqueous alkaline processing composition containing a silver halide developing agent and a silver halide solvent; reducing exposed silver halide to image silver; forming from unexposed and undeveloped silver halide a soluble silver complex; and transferring an imagewise distribution of this silver complex to a superposed silverreceptive stratum where it is reduced to image silver to form a positive silver transfer image.

Transfer processes for forming color images are also well known in the art. One such process, for example, described and claimed in US. Patent No. 2,983,606, relates to the formation of monochromatic or multicolor images by contacting each of one or more silver halide emulsions in an exposed photosensitive element with an aqueous alkaline processing composition containing a dye developer, i.e., a dye which is also a silver halide developing agent.

Generally speaking, a common denominator to all prior diffusion transfer processes is the presence of alkali in the processing fluid. The alkali is necessary to activate the processing composition since the developing agents commonly employed do not develop the latent image in the exposed photosensitive element unless the pH of the processing composition is sufiiciently high.

However, the incorporation in the developing composition of alkali presents certain inherent disadvantages,

3,362,823 Patented Jan. 9, 1968 chiefly the relative instability of alkaline compositions as compared to non-alkaline processing compositions, due primarily to oxidation. In addition, caustic processing baths present the inherent problems of corrosion and dangers resulting from spilling and/ or contact with the person.

The present invention obviates the aforementioned disadvantages by providing systems for preparing transfer images wherein non-alkaline processing compositions are employed.

According to the present invention, transfer images may be obtained by impregnating a photographic assemblage including an exposed photosensitive element and a superposed image-receiving stratum with an aqueous solution containing at least a photographically innocuous electrolyte, a silver halide developing agent, and a silver halide solvent, for example, by immersion; and thereafter bringing the impregnated assemblage in contact with a pair of electrodes so that a direct electric current is caused to flow through the assemblage (FIG. 1). This electric current generates hydroxyl ionsin situ, thus activating the developing agent and causing development and formation of the transfer image.

Any or all of the aforementioned ingredients of the processing composition may be present initially in the photographic assemblage, e.g., coated or encapsulated in one of the elements thereof, or they may be present initially in the aqueous impregnating medium.

As used herein the term photographically innocuous electrolyte is intended to define electrolytes which are not harmful or do not hinder the development process, although they may provide some additional function in the development and/or formation of a photographic image having the desired characteristics.

Useful electrolytes which would be photographically innocuous will be readily apparent to those skilled in the art and hence such materials per se comprise no part of this invention. As examples of useful electrolytes, mention may be made of the alkali metal sulfites, bisulfites, chlorates, chlorides, sulfates, etc.

As examples of useful developing agents, mention may be made of hydroquinone and derivatives of hydroquinones, such as, 4'-methylphenyl hydroquinone, etc., catechol and derivatives of catechol, such as 4-phenyl catechol, etc., derivatives of naphthol, such as 4-methoxyl-naphthol, derivatives of phenol, such as, methyl paraaminophenol sulfate, etc., the 3-pyrazolidones, such as 1- phenyl-3-pyrazolidone, etc.

In diffusion transfer processes for forming silver images, the processing composition should also contain a silver halide solvent. Suitable solvents, such as sodium thiosulfate, are also well known in the art, and it is also known in the art to incorporate such solvents, in whole or in part, in one or both of the sheets.

The present invention is particularly adaptable to automatic systems for document duplication and the like, wherein the photosensitive element or film assemblage is advanced from an exposure station to an impregnation station and finally to an electrolysis station to provide the desired reproduction of the original subject matter.

One useful electrolysis system is illustrated in FIG. 2. As shown therein, a pair of rollers 10 and 11 of a conductive material, such as steel, are connected by leads 13 and 14, respectively, to a suitable source of electric current 15 which may, for example, be a battery. By way of illustration, roller 11 is shown to be cathodic while roller 1% is anodic. A suitable current is impressed as the photographic assemblage 12 is advanced between the rollers, thus causing a direct electric current to flow through assemblage 12, thereby generating hydroxyl ions to initiate development and form the transfer image. It will be appreciated that the amount of current and speed of advancement of assemblage 12 through the rollers may vary Widely and the selection of the particular operating conditions will be apparent to those skilled in the art.

For purposes of illustrating the present invention in greater detail there will be described hereinafter its applicability to photographic systems such as are described and claimed in copending application Ser.. No. 519,995 filed concurrently in the name of Edwin H. Land, as a continuation-in-part of application Ser. No. 368,622, filed May 19, 1964, and copending application Ser. No. 519,- 884 filed concurrently in the name of Edwin H. Land and Leonard C. Farney, as a continuation-in-part of application Ser. No. 368,621 filed May 19, 1964.

As is disclosed in these applications, a photographic film assembly including a layer containing a light opacity providing material is exposed, e.g., to a light source on the same side of the support for the film assembly as the layer of opacity-providing material, and is then processed to form a negative image in the silver halide emulsion layer and a positive transfer image in a stratum situated above the layer of opacity-providing material. This material is present in an amount sufficient to mask effectively the negative image but not in an amount sufficient to preclude photoexposure of the light-sensitive materal in the film assembly, so that there is formed a composite print which contains both a negative and a positive image but which is viewable by reflection as a positive reproduction of the original subject matter.

In application Ser. No. 519,995, the layer of opacityproviding material is situated over a layer containing a light-sensitive silver halide emulsion; while in application Ser. No. 519,8 84, the material is situated in the same layer as the light-sensitive silver halide emulsion and may also be present in a second layer over the layer containing the silver halide emulsion.

Any of the aforementioned film assemblies may contain an outer layer comprising a silver receptive stratum, i.e., a stratum containing at least one silver precipitating agent, or the silver precipitating agent may be present initially in the processing composition.

Alternatively, as is described and claimed in copending application Ser. No. 519,886 filed concurrently in the name of Ronald P. W. Cieciuch, the silver precipitating nuclei may be generated in situ by impressing the electric charge, in lieu of being preformed and initially present in the film assembly or the processing composition.

According to the present invention, any of the aforementioned film assemblies may be exposed in the manner described in the aforementioned patent applications Ser. Nos. 519,995 and 519,884 and then developed by impregnation with a non-alkaline processing composition and impressing an electric charge to the impregnated film assembly in the manner heretofore described to form a composite print viewable as a positive reflection print.

The following examples show by way of illustration and not by way of limitation the practice of this invention.

EXAMPLE 1 A photographic film assembly comprising a support having thereon, in order, a first layer containing a light-sensitive silver halide emulsion and an opacifying material, a second layer containing an opacifying material, and a silver receptive stratum substantially equivalent to that described in Example 3 of the aforementioned application Ser. No. 519,884 was exposed for two seconds and the exposed sheet was passed at a rate 0.3 in./sec. through a process bath containing the following ingredients:

Water cc 550.0 Sodium sulfite g 11.2 Hydroquinone g 4.0 Metol g 1.2 Sodium thiosulfate g 2.0

The thus-wetted sheet was then passed between a pair of roller-electrodes such as is illustrated in FIG. 2 at a charge of volts and at a rate of 0.15 in./sec. to form a dense silver transfer image viewable as a positive reflection print.

Similar results were obtained employing processing compositions containing hydroquinone alone, Metol alone, or 4,6diamino-ocresol as the developing agent.

EXAMPLE 2 Example 1 was repeated, except that the wetted sheet was pressed between the roller electrodes at a charge of 35 volts and at a rate of 0.3 in./sec. to provide a silver image comparable to that obtained in Example 1.

EXAMPLE 3 Substitution of 15 g. of sodium sulfate decahydrate (Na SO .10H O) for sodium sulfite in the processing composition of Example 1 followed by electrolysis in the same manner provided a good silver image viewable as a positive reflection print.

EXAMPLE 4 Substitution in the process of Example 1 of the following processing composition:

Water cc 550.0 Sodium sulfate (decahydrate) g 15.0 Hydroquinone g 4.0 Sodium thiocyanate g 2.0

gave a good silver image of somewhat lower density.

U.S. Patent No. 3,113,910 discloses a process wherein an exposed light-sensitive silver halide emulsion layer is developed by electrolysis to form a negative image. However, it has never heretofore been contemplated to prepare positive silver transfer images in the manner described in the foregoing description and defined in the appended claims.

Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a diffusion transfer process wherein a photosensitive element comprising a light-sensitive silver halide emulsion is exposed and developed with an aqueous alkaline processing composition to reduce exposed silver halide to image silver to form a negative image while at substantially the same time forming an imagewise distribution of image-forming constituents in terms of unexposed areas, which constituents are transferred by imbibition to a superposed image-receiving stratum to form a visible image thereon; the improvement which comprises impregnating said exposed light-sensitive emulsion with an aqueous non-alkaline processing composition, and thereafter passing a direct electric current between said stratum and said emulsion While in superposition, thereby generating hydroxyl ions in situ, whereby to develop said negative image and to form said transfer image.

2. A process as defined in claim 1 wherein said current is applied by passing said emulsion and said superposed stratum between a pair of electrodes.

3. A process for forming a positive silver transfer image which comprises exposing a photosensitive element comprising a light-sensitive silver halide emulsion; impregnating said exposed emulsion with an aqueous non-alkaline composition containing an electrolyte, a silver halide developing agent and a silver halide solvent; impressing an electric current for a time and at a voltage sufficient to generate in situ hydroxyl ions necessary to activate said developing agent, thereby initiating development; reducing exposed silver halide to image silver while forming from unexposed silver halide a soluble silver complex; and transferring said complex, at least in part, to a stratum where it is reduced to form a positive silver transfer image.

4. In a photographic process wherein a layer containing a light-sensitive silver halide emulsion is exposed through a layer of a light opacity-providing material positioned thereover to form a developable image and said exposed emulsion layer is contacted with a developing composition to form a negative image in said light-sensitive 'layer and a positive transfer image on a stratum above said layer of said material, said layer of said material being present in an amount sufficient to mask efiectively said negative image while at the same time providing a background for said positive image thereover, thereby providing a composite print viewable by reflected light as a positive image; the improvement which comprises forming said composite print by contacting said exposed emulsion layer and said layer thereover with an aqueous non-alkaline processing composition; and thereafter passing a direct electric current therebetween, thereby generating hydroxyl ions in situ, whereby to develop said exposed emulsion and to form said composite print.

5. A process as defined in claim 4 wherein said contacting step is effected by permeating said processing composition through said layer containing said opacity-providing material to said emulsion layer.

6. A process as defined in claim 4 wherein said processing composition comprises an aqueous solution of an electrolyte, a silver halide developing agent and a silver halide solvent.

7. A process as defined in claim 4 wherein said passage of current is effected by passing said two layers between a pair of electrodes.

8. In a photographic process wherein a layer contain ing a light-sensitive silver halide emulsion and a light opacity-providing material is exposed to form a developable image and said exposed layer is contacted with a developing composition to form a negative image in said layer and a positive transfer image on a stratum above said layer, said material being present in an amount sufficient for masking eifectively said negative image while at the same time providing a background for said positive image thereover, thereby providing a composite print viewable by reflected light as a positive image; the improvement which comprises developing said exposed layer by contacting said exposed layer with an aqueous nonalkaline processing composition; and thereafter passing a direct electric current therebetween, thereby generating hydroxyl ions in situ, whereby to develop said exposed emulsion and to form said composite print.

9. A process as defined in claim 8 wherein said layer is contacted with said processing composition by permeation through a stratum thereover.

10. A process as defined in claim 8 wherein said processing composition comprises an aqueous solution of an electrolyte, a silver halide developing agent and a silver halide solvent.

11. A process as defined in claim 8 wherein said passage of current is eifected by passing said layer between a pair of electrodes.

References Cited UNITED STATES PATENTS 3,189,454 6/1965 Luckey et al. 96-29 XR 3,220,536 11/1965 Fairbank 96-29 3,301,772 1/1967 Viro 963 XR I. TRAVIS BROWN, Acting Primary Examiner. I. P. BRAMMER, Assistant Examiner. 

1. IN A DIFFUSION TRANSFER PROCESS WHEREIN A PHOTOSENSITIVE ELEMENT COMPRISING A LIGHT-SENSITIVE SILVER HALIDE EMULSION IS EXPOSED AND DEVELOPED WITH AN AQUEOUS ALKALINE PROCESSING COMPOSITION TO REDUCE EXPOSED SILVER HALIDE TO IMAGE SILVER TO FORM A NEGATIVE IMAGE WHILE AT SUBSTANTIALLY THE SAME TIME FORMING AN IMAGEWISE DISTRIBUTION OF IMAGE-FORMING CONSTITUENTS IN TERMS OF UNEXPOSED AREAS, WHICH CONSTITUENTS ARE TRANSFERRED BY IMBIBITION TO A SUPERPOSED IMAGE-RECEIVING STRATUM TO FORM A VISIBLE IMAGE THEREON; THE IMPROVEMENT WHICH COMPRISES IMPREGNATING SAID EXPOSED LIGHT-SENSITIVE EMULSION WITH AN AQUEOUS NON-ALKALINE PROCESSING COMPOSITION, AND THEREAFTER PASSING A DIRECT ELECTRIC CURRENT BETWEEN SAID STRATUM AND SAID EMULSION WHILE IN SUPERPOSITION, THEREBY GENERATING HYDROXYL IONS IN SITU, WHEREBY TO DEVELOP SAID NEGATIVE IMAGE AND TO FORM SAID TRANSFER IMAGE. 